Sewing machines include a cloth feeding mechanism that feeds a cloth in a horizontal direction. The cloth feeding mechanism includes a feed dog, and the cloth is fed in the horizontal direction by this feed dog that comes out from the opening of a needle plate. The cloth feeding mechanism includes a structure that drives the feed dog. For example, a structure is known in which a feed rod is coupled with a main shaft of a sewing machine, and this feed rod is linked with the feed dog via an eccentric cam to drive the feed dog. When the main shaft is rotated by the drive of the sewing machine, the feed rod is rotated, and thus the feed dog is moved while tracing a motion trajectory by the eccentric cam.
In addition, as the structures that drive the feed dog, some sewing machines are provided with a motor that moves the feed dog up and down, and a motor that moves the feed dog in the horizontal direction. By controlling those motors through the CPU of the sewing machine, the feed dog can be driven with a proper motion trajectory.
When sewing is performed by using a sewing machine, the level of which the feed dog gets into a cloth and force to move the cloth change due to the thickness of a cloth to be sewn and the material thereof, and the like. When the feed dog is not moved while drawing a proper motion trajectory relative to the cloth to be sewn, the cloth is shrunk, and the sewing quality decreases. Hence, the motion trajectory of the feed dog is adjusted in accordance with the thickness of the cloth.
According to the cloth feeding mechanism that utilizes the eccentric cam, however, it is necessary for an operator to manually adjust the eccentric cam to change the motion trajectory. Hence, adjustment of the eccentric cam is a burden operation for the operator, and it is necessary to adjust the motion trajectory of the feed dog every time the cloth to be sewn is changed. This makes the sewing work complicated. In addition, according to the cloth feeding mechanism that utilizes the eccentric cam, the upper shaft and the lower shaft operate in conjunction with each other, and thus the phase to feed the feed dog is unchangeable.
According to the cloth feeding mechanism that utilizes the motors, the motion trajectory is to be adjusted through the independent motors, and thus a phase difference may be caused relative to the upper shaft that drives the needle bar. Accordingly, it is difficult to move the cloth at the optimized phase.
The present invention has been proposed to address the above-explained problems of conventional technologies, and it is an objective of the present invention to provide a sewing machine provided with a mechanism that can control a timing at which a feed dog feeds a cloth without a complicated adjustment work.